Apparatus for making electrical resistors



Nov. 13, 1962 H. E. LLOYD ETAL 3,063,346

APPARATUS FORMAKING ELECTRICAL RESISTORS File i April 1, 1959 VOLTAGE SOURCE HAROLD E LLOYD E 5 JAMES L. OWENS INVENTORS.

.A TTORNE Y Patented Nov. 13, 1962 3,063,346 APPARATUS FOR MAKING ELECTRICAL RESISTORS Harold E. Lloyd and James L. Owens, Winston-Salem,

N.C., assignors to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed Apr. 1, 1959, Ser. No. 803,499 1 Claim. (Cl. 9011.52)

This invention relates to an apparatus for making electrical resistors and more particularly to an apparatus for progressively spiralling electrical resistors formed of a thin conductive film deposited on a cylindricalinsulating base.

In the manufacture of electrical resistors, such as deposited carbon'resistors, it is customary to provide aresistor blank having a cylindrical insulating base and a thin conductive film deposited thereon. Frequently this film is carbon or a carbon compound. Ahelical groove is progressively cut through this film from one end of the resistor blank toward the other by means of a cutting or grinding wheel. In known techniques the resistor blank is held against the cutting wheel with a predetermined pressure by the gravitational force of the resistor blank and a related fixture used to support and rotate the resistor blank for spiralling. However, this technique has not proved entirely satisfactory because the degree of control of pressure of the resistor blank against the cutting wheel coupled to each chuck, and a frame. Fixed to the frame are supporting means having apertures in one end thereof for holding each shaft for rotational, axial, and pivotal movement about a predetermined common axis. Means for removing a predetermined portion of the film, deposited on the article, a magnet for holding the article in a predetermined position, and means for moving the article out of the predetermined position upon the removal of the predetermined portion of the film are also provided.

More specifically, an apparatus for cutting aspiral in a resistor formed of a thin film ofcarbon deposited on a cylindrical insulating base may include a pair of chucks for gripping the resistor for rotational and axial movement, a pair of drive shafts coupled to each chuck for turning them in unison, and a frame. A pair of spaced supporting arms are each fixed to the frame and have an aperture in one end thereof for holding each shaft for rotational, axial, and pivotal movement about a predetermined common axis. A cutting wheel is provided for removing a predetermined portion of the carbon film, an electromagnet being used to hold the resistor in cutting engagement with the wheel with a predetermined pressure. Means are also provided for pivotally swinging the resistor out of engagement with the cutting wheel upon the removal of said predetermined carbon film.

A complete understanding of the invention may be had from the following detailed description of a specific embodiment thereof when read in. conjunction with the appended drawing, in which:

FIG. 1 is a front elevational view of a preferred emcircuit;

bodiment of the-invention showing. an-electri calcontrol FIG. 2 illustrates a sectional view of apparatus taken along line 2-2 of FIG. 1;

FIG. 3 shows a sectional view of another embodiment of the apparatus;

FIG. 4 illustrates a deposited carbon resistor of the type grooved to value by apparatus comprising this invention. 7

Referring to the drawing, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown' in FIGS. 1 and 3 a resistor blank 11 having a cylindrical base of insulating material, such as ceramic or the like, with a deposit thereon of resistance material possessing characteristics desired in the finished resistor. This resistance film may be carbon deposited on a cylindrical ceramic base by any one of several conventional depositing methods, such as by passing a controlled mixture of an inert gas and a hydrocarbon gas over .the heated blank in a controlled atmosphere.

The apparatus which comprises a portion of the preferred embodiment of the invention being substantially symmetrical, only the left side of the apparatus as viewed in FIG. 1 need be described hereinbelow. The resistor blank 11 is gripped for rotation by a chuck 12 coupled fixedly to one end of a first independent drive shaft 13,

the other end ofwhich is connected to a first universal joint 14. As best seen in FIG. 1, chuck 12 includes two generally cylindrical members having aligned, opposing axial openings therein adapted to receive and grip the ends of resistor blank 11. Such a chuck is well-known in theart ,to which the invention pertains, and one suitable form thereof may be seen in U.S.'- Patent 2,724,306 to V. A. Woodell '(FIG. 4). The universal joint 14 is fixedly engaged to a telescopic shaft 15 adapted for transverse .-movement which shaft is coupled to asecond universal joint 16. A second independent drive shaft 17 is coupled to the, joint 16,arrd is driven by a motor means 18. The motor means includes a gear arrangement, not shown, which transversely travels along splines, not shown, causingan arm 19 to move left or rightalong a splined guide rod 21 to obtain transverse motion of the resistor blank 11 with respect to the fixed position of a cutting wheel 22. As shown in FIGS. land 2, each first inde- -'pendent drive haft-13 is held for rotational and axial 22 which is rotated in a stationary position. Also, horizontal inward and outward movement of the chucks 12 for engagement and disengagement of the resistor blank 11 is provided by the arms 19 through a link connector, generally designated by the numeral 25, having an arm 26, a link 27 pivotally connected to one end of the arm 26, and another link.28 pivotally connected to the other end of the arm 26. The link connector 25 is rotated about a pivot 29 by means not shown.

The pivotal movement of the arms 19 about a pivot 31 (FIG. 2) is controlled by a solenoid 32 fixed to the frame 24, the solenoid having an armature 33 connected pivotally to a lever arm 34. Thelever arm 34 is coupled to the splined guide rod 21 to impart rotation to it upon vertical movement of the armature 33. Such rotational movement of the splined guide rod 21 is transmitted to the arms 19 to cause them to rotate, for example, in the direction of the arrowshown in FIG. -2, which is away from the cutting wheel 22.

An electromagnet, generallyvdesignated by the numeral 35, having a magnetizing coil 36 fixed to the frame 24 by appropriate means, not shown, a core 3-7, and an armature 38 fixed to one of the arms 19, controls the pressure between .the ,resistor blank 11 and the cutting wheel 22. This pressure varies in accordance with the magnetic field strength ,of the electrornagnet 35, which field strength is dependent upon the electrical current through the magnetizing coil36. The current is controlled by a battery 39, FIG. 1 and a variableresistor 41, both of which are connected electrically in series with the magnetizingcoil 36 by conductors 42. ,It is apparent that the current of the magnetizing coil 36 can be controlled bythe variable resistor .41 to control the magnetic field strengthof the magnetizing coil 36 soias to regulate the pressure between theresistor blank 11 and the cutting wheel .22.

A control circuit, designated generally by the numeral v43, is connectedelectrically'to'the resistorblank 11'by conductors 44, slip.rings.45,.shafts 13, and chucks 12. The arms 19 are appropriately insulated from-the shafts 13'so as not to short-circuit.the-resistor blank 1'1.

The control circuit 43 includes a conventional Nl/heatstone bridgehaving fixedresistors 46,47, and 4 8 in .three branches thereof. The resistor blank ;11 makes up the fourth branch of the'bridge.

Battery 49 is connected electricallytothe bridge in .a conventional manner. Connected across the bridge I by conductors 51 is -a DC amplifier 52 which is coupled to anormally closed relay53'-by.conductors 54. Avoltage source 55 is connectedinserieswith the contacts ofthe relay 53 and the solenoid 32-byconductors56.

Referring to the embodimentshown'in FIG. .-3, an electromagnet 57 includes a'magnetizingcoil 58 i fixed to. the frame 24 by appropriate means, not shown, a core 59, and

I pivot 31.

Itshould be understood thatin-either; of the embodi- -rnents ofFIGS.-;l-and3, a permanent magnet could be substituted for theelectr'omagnet 35 if a great degree of control of pressure between the resistor blank 11-Iand the cutting wheel 22 is considered unnecessary.

OPERATION The resistor blank 11 to be helically grooved orspiralled to value is positioned within the chucks 12 by actuating a rotating means, not shown,-to pivot the arm 26.of..-the link connector'25 in a clockwise direction about the pivot .29 thus moving axially the arms-19 and chucks 12 r away from each other. While the chucks-12 are in this position the resistor blank ll is axially-aligned with the common horizontal axis of chucks 12 by holding means, not shown.

The rotating means is again actuated to'rotate the arm 26 .of the link connector in-a counterclockwise direction to move the chucks 12 along their commonaxis to grip the resistor blank ll for rotation. 7

After the resistor blank 11 is'gripped by the chucks 12, one end of the resistor-blank 11 is attracted and held against the vcutting wheel-22 by the electromagnet as shown in section inFIG. 2. The variableresistor 41 is adjusted to control the field strengthof the magnetizing coil 36 to obtain'the desired pressure between the resistor blank 11 and the cutting wheel 22. 7

Before thehelical grooving is begun, control means, not shown, guide the second independent drive shafts 17 such that the left end of the resistorblank 11 engages the cutting wheel 22. At this time'the left telescopic shaft 15 is axially extended and the right, telescopic shaft 15 is foreshortened.

With the resistor blank 11 positioned within the chucks 12, it becomes one branch of the Wheatstone bridge and as such causes a bridge unbalance. Bridge resistors 46,

47, and 48 are of such a predetermined fixed value that the bridge will balance when the helical groove of the resistor blank 11 has advanced an extent necessary to achieve the desired resistance value. The bridge unbalance caused by the ungrooved resistor blank 11 causes a voltage across the center branch of the bridge which is amplified by the DC. amplifier 52 thereby impressing a voltage across the normally closed relay 53. The impressed voltage opens the contacts of the relay 53 to prevent any voltage from the source 55 from being impressed across the solenoid 32, thus maintaining it inoperative when the relay 53 is operative.

With the second independent driving shafts 17 and the electromagnet 35 maintaining one end of the resistor blank 11 in engagement with the cutting wheel 22, the helical grooving operation is begun by simultaneously actuating the respective independent motor means 18 to .rotate the resistor blank 11 and by actuating driving .means, not shown, to rotate the cutting wheel 22. Thus ,ahelicalzgroove 62 is progressively cut through the film ofthe resistor blank '11. As the groove 62jis progressively cut from the end ofthe resistor blank 11 to the other, the

,electrical resistance of the resistor blank 11 increases untilthe Wheatstone bridge is in balance, at which time ,the tbridge output:falls to zero. With zero output from the bridge, thenormally closed relay '53 becomes inoperative thereby closing its contacts. When these contacts are closed, a voltagefrom the source 55 is impressed across .the solenoid 32to move thearmature 33 upwardly. Hence the-lever arm 34, the ar ms 19,, the first independent driv- -ing shafts 1 3, the chucks .12, and theresistorblank 11 .are pivoted counterclockwise, asshown-by the arrow of FIG. 2, away from the cutting wheel 22. ,The force piv- .oting the resistor blank 11 out of cutting engagement with 'the yyheel 22 i s large enough to overcome the magnetizing force of the electromagnet 35. Thus the resistor blank 11 has been; helically, grooved to v a predetermined. resistance ,value. i

Theernbodiment of FIG. .3 operates similarly tothat of FIGS. 1 and 2 except that upon Wheatstone bridge It should be understood that the above-described embodiment of the invention is merely illustrative and that numerous modifications may be made within the spirit andscope of the invention. Further, the particular apparatus illustrated is only one example of several types of apparatus which may be included in practicing the invention and the invention is not limited solely to the use of this apparatus. -What is claimed is: In an apparatus for progressively cutting a helix in a .resistor formed of a thin film of carbondeposited on a cylindrical insulating base, a pair of chucks for gripping the resistor-for rotational and axial movement, a pair of shafts for simultaneously rotating and axially moving ,eachchuck, a frame, a first and second supporting arm,

eachv having an aperture in one end thereof for holding each shaft for simultaneous rotational and axial movement about a predetermined common axis, means for pivotally mounting the supporting arms to the frame, a cutting wheel for removing a portion of the film, the combinationiwith said first and second supporting arms of an electromagnet having an operating coil fixed to the frame and a coacting armature fixed to the first supporting arm for attracting and holding the resistor in engagement with the cutting wheel, electrical supply means for energizing the electromagnet, a variable resistor in series with the supply means for controlling the magnetic field strength of the electromagnet, thereby controlling the pressure between the resistor and the cutting wheel, a Wheatstone I 8,063,846 5 6 bridge having the resistor to be helixed connected in one circuit for energizing the operating coil of the solenoid branch thereof and normally having a voltage output, a to diseng ge the resistor and cutting ee normally open circuit, a relay responsive to the absence of a bridge output for closing said circuit, a solenoid having References Cited in the me of this P an operating coil fixed to the frame and a coacting arma- 5 UNITED STATES PATENTS ture fixed to the first arm and having said circuit in series 2,623,439 Paskell D 30, 1952 with said operating coil, and a voltage source rendered 2,724,306 w n No 22, 1955 effective by the operation of the relay and closing of the 2,773.332 Bachman et aL Dec 11, 1956 

